This research project is concerned with two major subjects: One is the electrophysiological studies of the sympathetic pre- and postganglionic neurons in reference to the membrane characteristics, the mechanisms underlying synaptic transmission and modulation, and the mechanisms regulating the presynaptic innervation and distribution of subsynaptic sites. The following are the specific aims in this subject set for 1973/1974. 1) Determination of the exact location and distribution of nicotinic and muscarinic receptor sites on the isolated amphibian and mammalian sympathetic ganglion cells. 2) Investigation of the mechanisms underlying the facilitation and depression of synaptic transmission in amphibian sympathetic ganglia by means of a voltage- clamp technique. 3) Studies of the ionic requirements for the production of various synaptic and nonsynaptic activities of sympathetic ganglion cells. The other subject is concerned with the physiological and pharmacological nature of the GABA (gamma-aminobutyric acid) receptors on the amphibian and mammalian primary afferent neurons. This study is aimed to clarify the ionic mechanism underlying the GABA receptor interaction, and the interaction between GABA and antagonists. This basic information will be applied to elucidate the mechanism underlying the presynaptic inhibition in the spinal cord and higher centers.